The exchange of strands between two identical or homologous double stranded DNA molecules is an important phenomenon in DNA recombination, replication and the formation of cruciform structures in development. This process involves the formation of a junction structure, consisting of four double helices, two before and two after the site of strand exchange, which is termed the branch point. Branch point migration is the movement of this point through space as the strands are exchanged. Although several models exist for the detailed geometry of this system, almost no experimental data exist to support or refute them. What has been lacking, to date, has been a tractable experimental system for studying the 3-dimensional structure, molecular-dynamics and thermodynamics of multi-stranded recombinational intermediates. This is because the migration rate for a branch point is about 6000 base transitions/sec. We have managed to devise a system which should immobilize these intermediates. By utilizing such a system, we hope to study both the structural and the dynamical parameters which characterize the exchange of DNA between double helices, during recombination. The means by which we will characterize the structural aspects of the intermediates will involve both solid state analysis by means of x-ray crystalolography, and solution analysis via spectroscopic procedures. Spectroscopic techniques, such as absorbance and Nuclear Magnetic Resonance will be used to characterize the dynamical parameters of the system about its equilibrium point. Furthermore, the system will permit the rapid determination of the effects of drugs and environmental-chemicals on the migration rate. The quarter century of lore which has been accumulated for the study of the physical properties of double-stranded nucleic acids will all be applicable to this new system.